Reflectors are used whenever a light source emits light omnidirectionally or else over a solid angle which is not suitable for the intended purposes.
Reflectors are, as preferably also provided in the present instance, often manufactured from a stable base material onto which a reflective layer is applied. The reflective layer points toward an interior space which is provided to hold a lamp.
The shape of conventional reflectors, in particular of the contour of the reflective surface, is based on conic sections. A section through the reflector reveals a conic section in this case. As a rule the reflector is a rotational body of a conic section. Conventional reflectors thus have for example the shape of a paraboloid (rotational body of a parabola) or of an ellipsoid (rotational body of an ellipse). Parabolic reflectors and ellipsoidal reflectors can advantageously be used if the light needs to be strongly parallelized (parabolic reflector) or focused (ellipsoidal reflector).
There are however applications in which the light from the lamp is not to be focused as strongly as possible but is to be concentrated onto a somewhat more extensive area. This is the case for example with regard to projector apparatuses, or if the light is to be coupled into a glass fiber. In these cases the so-called etendue (light-gathering power) is used as a parameter. The etendue is a parameter for an optical system, for example a light source, a lamp having a reflector situated around it being regarded overall as a light source in the present case. The surface onto which the reflector concentrates the light of the lamp is seen as the emitting surface of the light source. If the solid angle is also included, the etendue can be calculated. The etendue is a conserved quantity (Lagrange invariant) in all optical systems. The reflectors based on conic sections are not completely satisfactory in applications in which a certain etendue is specified.
In the technical field there has been a shift toward departing from the conic section shapes. The documents WO 2007/081812 A2, CA 2071635 C, EP 519112 A1, U.S. Pat. No. 4,355,350 A, U.S. Pat. No. 5,661,828 A and U.S. Pat. No. 6,547,416 B2 may be referenced by way of example.